The present invention relates generally to the field of bioseparation, and in particular to the field of biological sample processing.
Sample preparation is a necessary step for many genetic, biochemical, and biological analyses of biological and environmental samples. Sample preparation frequently requires the separation of sample components of interest from the remaining components of the sample. Such separations are often labor intensive and difficult to automate.
In many cases it is necessary to analyze relatively rare components of a sample. In this case, it may be necessary both to increase the concentration of the rare components to be analyzed, and to remove undesirable components of the sample that can interfere with the analysis of the components of interest. Thus, a sample must be “debulked” to reduce its volume, and in addition subjected to separation techniques that can enrich the components of interest. This is particularly true of biological samples, such as ascites fluid, lymph fluid, or blood, that can be harvested in large amounts, but that can contain minute percentages of target cells (such as virus-infected cells, anti-tumor T-cells, inflammatory cells, cancer cells, or fetal cells) whose separation is of critical importance for understanding the basis of disease states as well as for diagnosis and development of therapies.
Filtration has been used as a method of reducing the volume of samples and separating sample components based on their ability to flow through or be retained by the filter. Typically membrane filters are used in such applications in which the membrane filters have interconnected, fiber-like, structure distribution and the pores in the membrane are not discretely isolated; instead the pores are of irregular shapes and are connected to each other within the membrane. The so-called “pore” size really depends on the random tortuosity of the fluid-flow patches (e.g. pores) in the membrane. While the membrane filters can be used for a number of separation applications, the variation in the pore size and the irregular shapes of the pores prevent them being used for precise filtration based on particle size and other properties.
Microfabricated filters have been made for certain cellular or molecular separation. These microfabricated structures do not have pores, but rather include channels that are microetched into one or more chips, by using “bricks” (see, for example, U.S. Pat. No. 5,837,115 issued Nov. 17, 1998 to Austin et al., incorporated by reference) or dams see, for example, U.S. Pat. No. 5,726,026 issued Mar. 10, 1998 to Wilding et al., incorporated by reference) that are built onto the surface of a chip. While these microfabricated filters have precise geometries, their limitations are that the filtration area of the filter is small, limited by the geometries of these filters, so that these filters can process only small volumes of the fluid sample.
Blood samples provide special challenges for sample preparation and analysis. Blood samples are easily obtained from subjects, and can provide a wealth of metabolic, diagnostic, prognostic, and genetic information. However, the great abundance of non-nucleated red blood cells, and their major component hemoglobin, can be an impediment to genetic, metabolic, and diagnostic tests. The debulking of red blood cells from peripheral blood has been accomplished using different layers of dense solutions (for example, see U.S. Pat. No. 5,437,987 issued Aug. 1, 1995 to Teng, Nelson N. H. et al). Long chain polymers such as dextran have been used to induce the aggregation of red blood cells resulting in the formation of long red blood cell chains (Sewchand L S, Canham P B. Modes of rouleaux formation of human red blood cells in polyvinylpyrrolidone and dextran solutions 1979 57(11):1213-22). However, the efficiency of these solutions in removing red blood cells is less than optimal, especially where the separation or enrichment of rare cells, such as, for example, fetal cells from maternal blood or cancer cells from a patient, is desirable.
Exfoliated cells in body fluids (e.g. sputum, urine, or even ascetic fluid or other effusions) present a significant opportunity for detection of precancerous lesions and for eradication of cancer at early stages of neoplastic development. For example, urine cytology is universally accepted as the noninvasive test for the diagnosis and surveillance of transitional cell carcinoma (Larsson et al (2001) Molecular Diagnosis 6: 181-188). However, in many cases, the cytologic identification of abnormal exfoliated cells has been limited by the number of abnormal cells isolated. For routine urine cytology (Ahrendt et al. (1999) J. Natl. Cancer Inst. 91: 299-301), the overall sensitivity is less than 50%, which varies with tumor grade, tumor stage, and urine collection and processing methods used. Molecular analysis (e.g. using in situ hybridization, PCR, microarrays, etc) of abnormal exfoliated cells in body fluids based on molecular and genetic biomarkers can significantly improve the cytology sensitivity. Both biomarker studies and use of biomarkers for clinical practice would require a relative pure exfoliated cell population enriched from body fluids comprising not only exfoliated cells but also normal cells, bacteria, body fluids, body proteins and other cell debris. Thus, there is an immediate need for developing an effective enrichment method for enriching and isolating exfoliated abnormal cells from body fluids.
Current approaches for enriching and preparing exfoliated cells from body fluids are through media based separation, antibody capture, centrifugation and membrane filtration. While these techniques are simple and straightforward, they suffer from a number of limitations, including: inadequate efficiency for rare cell enrichment; low sensitivity of rare cell detection; difficulty in handling large volume samples; inconsistency of the enrichment performance; and labor-intensiveness of separation procedure.
There is a need to provide methods of sample preparation that are efficient and automatable that can process relatively large sample volumes, such as large volumes of biological fluid samples, and separate target cells. The present invention provides these and other benefits.